The present invention relates to rotary mills. More particularly, the invention relates to an automated system for reliably discharging rotary mills.
Rotary mills, also known as ball mills, pebbles mills, rod mills, or tumble mills, are well known in the art. A traditional rotary mill includes a horizontal rotating cylinder that rotates about a central axis. The cylinder includes grinding media that is generally spherical, cylindrical, or another uniform shape. Solid target materials are placed, as a dry solid or along with a liquid medium, into the cylinder for milling. The cylinder is rotated, causing the grinding media to tumble along with the target material, with the grinding media abrading and impacting the target solids. Continued rotation of the cylinder results in a milled product in the form of dry fine particles or particles suspended in liquid media.
Upon completion of the milling process, the product is discharged from the cylinder. The cylinder includes an opening with a solid cover that can be manually removed and replaced with a discharge grate, which will retain the grinding media but allow the product to pass through.
In the case of dry product, the product can become trapped between grinding media when the cylinder is stationary. Thus, to discharge the product, the cylinder can be rotated with the discharge grate open to discharge the solid product. In the case of a wet product, the cylinder can remain stationary if the liquid suspending the product is low-viscosity to flow past the media due to gravity. In the case of non-Newtonian or high-viscosity liquids, the cylinder can be rotated to discharge the product, similar to dry product.
In another form, the grinding media and product can be dumped from the cylinder without the use of a grate, and subsequently separated by a grate, filter, or vibrating sifter.
The rotary mill also includes a discharge housing that surrounds the rotating cylinder to define an annular space between the cylinder and the housing. The housing also includes a collection hopper at the bottom. When the product is discharged, as described above, the product will enter the annular space and fall into the hopper.
However, the above discharge process can result in dirty conditions, with dust becoming adhered to the inner surface of the housing as well as the outside of the cylinder. Retrieval of the product from the discharge housing can also result in dust entered the surrounding air. These conditions can reduce the amount of product recovered, as well as lead to cross-contamination issues and cleaning problems. In the case of liquid product, the operator must make and break a piped connection to the discharge housing, exposing the milled product and solvent vapors to the surrounding area during this connection.
Accordingly, there is a need for a discharge system that can reliably deliver the milled product from the cylinder while limiting loss of product and exposure of the product to adjacent areas and operators.